1. Field of the Invention
This invention relates to a method of controlling a rolling mill, and more particularly to a method of setting and controlling unequal circumferential speed rolling which uses a rolling mill with work rolls rotating at different circumferential speeds.
Usually, a rolling mill is operated with the upper and lower work rolls rotating at the same revolution speed and a possible thickness limit of rolled sheet is several hundred micrometers at the thinnest. However, recently a rolled sheet thinner than this limit has been in demand, and it has been said that unequal circumferential speed rolling is suitable for a rolling method which will meet this current demand.
However, a control method for this unequal circumferential speed rolling has not been established yet. In order to establish a computer system for the unequal circumferential speed rolling similar to that of the conventional equalized circumferential speed rolling, it is necessary to establish methods of controlling the setting of a rolling mill, and the thickness, the tension or the adaptability of a work during rolling.
2. Description of the Prior Art
The unequal circumferential speed rolling, in which the controlling parameters have a complicated influence on each other, requires a different control method from that for the equalized circumferential speed rolling. Though in the actual rolling, setting up is an important factor, no report has been found which explains the setting up of the unequal circumferential speed rolling.
In U.S. Pat. No. 4,145,902 a rolling method is disclosed in which a rolling load is reduced without using an RD (Rolling Drawing) rolling in which a sheet is wound around a roll. That is, in that method, the upper and lower work rolls are controlled such that the ratio of their circumferential speeds is equal to the ratio of elongation of a rolled work, the outlet speed of the work is equal to the circumferential speed of the higher speed roll, and its inlet speed is equal to the circumferential speed of the lower speed roll.
In U.S. Pat. No. 4,145,901, in addition to the patent above described, it is disclosed that a tension limit device and a computer are provided such that when the tension is beyond the limit value, the computer revises the roll position in correspondence with the rolling reduction, and further, in this patent, speed control and tension control over the rolling stands which are adjacent to each other are described.
In the present state of the art, however, in this kind of control, due to the mutual interference of other parameters, the setting of the speeds of a pair of work rolls and the setting of the rolling position are determined by trial and error. PG,4
In computer control, it is a great problem that a setting operation cannot easily be determined, and therefore establishment of a set-up control method suitable for computer control for the unequal circumferential speed rolling is desired.